1. Field of the Invention
The present invention relates generally to intraluminal stents. More particularly, the present invention provides devices and methods which allow for localized delivery of bioactive compounds.
Many diseases may cause body lumens to undergo stenosis. Probably the most common is atherosclerosis. Atherosclerosis is a condition which commonly affects the coronary arteries of the heart, the aorta, and the carotid arteries. Atherosclerotic plaques of lipids, fibroblasts, and fibrin proliferate and cause obstruction of the artery. As the obstruction increases, a critical level of stenosis is reached which does not allow sufficient blood flow to pass the obstruction to meet the metabolic needs of tissue distal to the obstruction resulting in ischemia. Atherosclerotic plaques also have the potential for rupture which can expose the flowing blood to a strong procoagulant stimuli often resulting in thrombus formation. Thrombus formation in the coronary circulation leads to unstable angina and myocardial infarction. Thrombus formation in the cerebral circulation leads to stroke, TIA (transient ischemic attack) and RIND (reversible ischemic neurologic deficit).
Many therapeutic alternatives are available for the treatment of atherosclerotic diseases, including surgery and medical treatment. One particularly useful therapy for selected atherosclerotic lesions is percutaneous transluminal angioplasty. During angioplasty, a balloon tipped catheter is inserted in an artery of the patient with the balloon deflated. The catheter tip is advanced to the site of the atherosclerotic plaque to be dilated. The balloon is placed within the stenotic segment of the artery and inflated. During inflation the plaque "cracks" and the vessel expands, at least partially relieving the stenosis.
While angioplasty has gained wide acceptance, it suffers from two major problems, i.e. abrupt closure and restenosis. Abrupt closure refers to the acute occlusion of a vessel immediately after or within the initial hours following a dilatation procedure. Abrupt closure occurs in approximately one in twenty cases and frequently results in myocardial infarction and death if blood flow is not restored in a timely manner. The primary mechanisms of abrupt closures are arterial dissection and/or thrombosis. It is postulated, that the ability to deliver agent (e.g. antithrombotic) directly into the arterial wall at the time of angioplasty could reduce the incidence thrombotic acute closure.
Restenosis refers to the re-narrowing of an artery after an initially successful angioplasty. Restenosis occurs within the initial six months after angioplasty and is due to the proliferation and migration of the cellular components of the arterial wall. It is postulate that the delivery of agent(s) directly into the arterial wall would interrupt the cellular events leading to restenosis.
Medical prevention of abrupt closure and restenosis has not been entirely successful. Endovascular stents have been placed in the dilated segments to mechanically block abrupt closure and restenosis. Unfortunately, such stents have a high rate of thrombotic abrupt closure and have not significantly reduced restenosis.
Non-atherosclerotic vascular stenosis may also be treated by angioplasty. For example, Takayasu arteritis or neurofibromatosis may cause stenosis by fibrotic thickening of the arterial wall. Restenosis of these lesions occurs at a high rate following angioplasty, however, due to the fibrotic nature of the diseases. Medical therapy has been similarly disappointing.
What is needed in the art are devices and methods for the prevention of abrupt closure and/or restenosis following dilation of blood vessels. In particular, it would be desirable to provide devices and methods which can provide antithrombic and other medications to regions of a blood vessel which have been treated by angioplasty or other interventional techniques, such as atherectomy, laser ablation, or the like. Such devices should be capable of providing both short term medication delivery, over the initial hours and days after the treatment, as well as long term medication delivery, over the weeks and months after the treatment. Surprisingly, the present invention fulfills these and other needs.
2. Description of the Background Art
U.S. Pat. No. 4,300,244 describes an endovascular prosthesis which may be coated with carbon for biocompatibility. U.S. Pat. No. 4,580,568 describes endovascular stents which are formed of stainless steel in a zig-zag pattern. U.S. Pat. No. 4,733,665 describes expandable intraluminal vascular grafts placed by balloon angioplasty catheters. U.S. Pat. No. 4,739,762 describes expandable intraluminal grafts which may have a plurality of slots in the graft walls. U.S. Pat. No. 4,776,337 describes expandable intraluminal stents coated with a biologically inert substance, such as polyurethane or other inert plastics. U.S. Pat. No. 4,800,882 describes an expandable endovascular stent formed from wire bent into serpentine configurations. U.S. Pat. No. 4,990,155 describes a plastic coil for use as an endovascular stent to prevent restenosis following angioplasty. U.S. Pat. No. 5,019,090 describes radially expandable endoprostheses. U.S. Pat. No. 5,053,048 describes thromboresistant coating which may be applied to intravascular stents. U.S. Pat. No. 5,059,211 describes expandable endovascular stents which are bioabsorbable. Each of the above references is incorporated herein by reference.
PCT Application No. 92/11895 describes a balloon catheter capable of releasing drugs directly to tissue in a body lumen wall. PCT Application No. WO 92/11890 describes a balloon catheter having a coating of body affecting chemicals which are released when the balloon is inflated and contacted with body lumen walls. PCT Application No WO 87/04935 describes spring coil intravascular stents. European Patent Publication No. 281,482 describes preparation of biodegradable polymers. European Patent Publication No. 433,011 describes an intra-arterial stent which incorporates or is coated with a radioisotope. Chasin et al., "Polyanhydrides as Drug Delivery Systems" in Biodegradable Polymers as Drug Delivery Systems, Langer and Chasin, eds., Mercel Dekker, Inc., 1990, pp. 43-70; Langer, Science, 249:1527-1532; and Langer and Moses, J. Cell. Biochem., 45:340-345 describe biodegradable materials useful in drug delivery systems. Each of the above references is incorporated herein by reference.